Hydroclimate And Ecosystem Changes In Alpine Canyon Area,Southwestern China Over The Past Decades

The global and regional climate have experienced considerable changes over the past decades especially precipitation and temperature which influence on hydrological cycle.Therefore,studying responses of hydrological cycle?evapotranspiration?to climate change has attracted much attention.Moreover,China is one of the most countries affected by drought and warming due to the significant increasing trend of precipitation and temperature.Droughts are the world's most damaging and pressing natural disasters and causing tens of billions of dollars in global damages,and collectively affecting more people than any other form of devastating climate-related hazards.Examining ecosystem distributions and dynamics and identifying their relationships with climate will contribute to a better understanding of the interactions among climate,human activities,and ecosystem variation,and facilitate the design,planning and implementation of ecological reconstruction projects in southern China.On contrast,the quantitative assessment of the environmental impacts on river basin management is critical to reveal the characteristics of runoff change and thus solve the water resource management issues that has become a popular topic in hydrological research.Hence,the knowledge of contribution of climate change to runoff is essential for ecological environment protection and water resources management.Thus,the objectives of the study were:1)to quantify the relationship between ecosystem and climate variables,2)to investigate the coupling between drought and water use efficiency,and 3)to assess the water resources risk management strategy in the Lancang and Jinsha rivers.Based on multi-source datasets,including observational climate and runoff data,satellite remote sensing images?MODIS and Landsat?.The observed ecosystem data and human activities datasets over the past 60 years were used.The study quantified the relationship of variables between ecosystems,climates and human activities through various integrated approaches,including spatiotemporal interpolation,Penman-Monteith,Mann–Kendall test,correlation analysis,transition matrix,principle component analysis and a slope changing ratio of cumulative quantity approach.The results of the study were summarized below:?1?Climate factors have changed significantly over the past 60 years in southwest China.The changes of the evapotranspiration?ET₀?were greatly influenced by the combined effects of precipitation?with a decrease rate of 13.7 mm/10-years?and temperature?with a decrease rate of+0.17?/10-years?which increased the annual average ET₀?by+2.1 mm/10-years?.Maximum temperature was the most contributor to ET₀,followed by solar radiation and vapor pressure deficit.?2?Southwestern China had suffered an increasing serious drought.The analysis of drought index of SPI-6 revealed that more than 20%of the total area was categorized as extreme droughts.During 16-years,WUE had decreased by-0.8 g C/kg H₂O,the average annual WUE was 2.37 g C/kg H₂O.The correlations between drought index and water use efficiency?WUE?presented a large spatial heterogeneity which ranged from-0.4 to 0.6.?3?Ecosystems were obviously affected by climate change,especially the relatively large rising temperature.After 2000,the areas of both agriculture and grassland decreased;but forest area increased due to water resource protection,urban expansion and implementation of ecological projects“Grain for Green Project”.?4?Socioeconomic development and the dam's construction in southwestern China impacted runoff changes.The average annual runoff exhibited a non-significant decreasing trend from upstream to downstream over the Lancang and Jinsha rivers with a rate of-26.3mm/10 year.The runoff had a sharp decrease in drought years.In the Lancang River,the average contributions of climate change and human activities were 6%and 94%,respectively.For the Jinsha River,the average contributions of climate change and human activities were-50%and 150%,respectively.These results suggested that human activities highly contributed to the runoff changes over the Lancang River and Jinsha River.The results of this thesis have implications for ecosystem management and climate policy.First,improving the weather modifications,water conservation,water-saving technology and effective drought management practices that can save the water resources in the rainy seasons,also it helps the drought in the dry seasons and face the future water resources shrinkages.Second,applying a comprehensive assessment model to select the plant species in ecological restoration areas,which finally have implications for environmental protection,water resources management and ecological restoration in the southwest of China's rivers.